[Haskell-cafe] bitSize

Quoting the Haddock documentation for Data.Bits.bitSize: "Return the number of bits in the type of the argument. The actual value of the argument is ignored. The function bitSize is undefined for types that do not have a fixed bitsize, like Integer." Does anybody else think it would be *far* more useful if bitSize applied to an Integer would tell you how many bits that particular Integer is using? Especially given that it can vary? Is there a way to actually determine how many bits are in an Integer?